Crashes related to video playlist

CPU - i5 3450
GPU - GTX960 2GB

So here’s the issue. This is actually my first time editing a long video which is about 20 minutes.
At some point, I needed to edit the speed of my video. So I adjusted video speed and follwed by instant crash.
Tried again but no luck. Took a look at task manager to see some sort of strange behaviors. nothing,
It seems either Shotcut or my computer couldn’t handle the amount of work it needs to do.

Strangely enough, removing 20 minutes of long raw unedited 8GB video from the playlist solved the issue.
kinda makes sense but I’d like to know what’s up.

thanks for reading